This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
The invention addresses the problem of allocating radio resources on the uplink in an OFDMA system. In an OFDMA system, such as the uplink of IEEE 802.16e otherwise known as WiMAX, power control is typically employed to prevent large variations in received signal strength across frequency sub-carriers at the receiver. However, some fraction of user terminals in the cell may be in a disadvantaged situation whereby their maximum transmit power is lower than that required to meet the power control criterion. Such, user terminals are power-limited and simply transmit at maximum power. As the difference between the power required to meet the power control criterion and the maximum transmit power increases, the SINR for the user terminal reduces as well. In an OFDMA system, the bandwidth allocated to the user may be varied. Lowering the bandwidth allocated to power-limited user terminals improves their signal to impairment ratio resulting in a higher probability of error-free communication, albeit at a potentially lower rate. The number of bits per transmitted symbol is determined by the modulation and coding scheme (MCS). Each MCS has an SINR threshold above which the block error rate is lower than some pre-specified criterion. Given a requested number of bits to be transmitted by the user terminal, a radio resource allocation must be determined. The resource allocation consists of a specified number of slots and a specific MCS assignment to use in those slots. A slot is a time-frequency resource block with a number of slots concatenated in time forming a subchannel. The number of slots per subchannel depends on deployment parameters. For power-limited user terminals, the MCS assignment depends on the SINR, which depends on the number of subchannels assigned, which in turn depends on the number of bits to be transmitted and the MCS used. Thus, there is a circular interdependence among criteria used to decide the various components of the radio resource allocation in the uplink of an OFDMA system. This leads to the following observations:                1. For some packet sizes, there are cases where a MCS corresponding to a higher transmission rate is always more beneficial to use than one corresponding to a lower transmission rate.        2. Fragmentation of packets that are not delay-sensitive allows optimizations leading to greater spectral efficiency.        
This invention solves the problem of allocating radio resources in such a system taking these factors into account.